There have been major recent advances in our understanding of smooth muscle excitation mechanisms. Results from this project have established that Hodgkin-Husley-like ionic conductances account for the action potential and furthermore the unique spontaneous electrical behavior of smooth muscle has been suggested by others to have both an electrogenic pump component and voltage dependent ionic conductances. While we have a general outline of the nature of smooth muscle electrical activity, we are far from a complete quantitative description. A major technical problem, of course, is the small size of single mammalian smooth muscle cells and the compromising problems of tissue geometry when multicellular preparations are used. This project has been committed to the development of quantitative voltage-clamp procedures. A recent major effort is in the area of single isolated cell voltage-camp. Amphiuma stomach smooth muscle cells are being used in the development of this technique.